i have this issue too. i spawned in 2 dragons and tamed them, and they do not have the hearts/mate boost and i can't breed them. a server restart the other day fixed the issue, but i spawned one in last night and she is not boosted like the other ones were.

If you force spawn them there is an issue. However a wild one tamed that spawned naturally will have no problems. We tested this the other night.

-=Justicel=- (Firehawk) の投稿を引用：

If you force spawn them there is an issue. However a wild one tamed that spawned naturally will have no problems. We tested this the other night.

I've noticed this, too.
Some of my dragons on the server seem to have gone sterile. They have a mate boost and will mate with other dragons but no egg is produced and we're stuck with an ugly cooldown timer.
I had a friend spawn a few dragons to test to see if they would lay eggs and they would. They were even mate boosted by other older dragons that were actually natural spawns.
However, when I got on to do it (only an hour later) it had all changed. Dragons I spawned would not be mate boosted by older dragons. When my friend came back on to try, the dragons spawned by them were also not mate boosted.
It started very suddenly and now we're stuck with some dragons that are mate boosted and some that just aren't for no explained reasons. We're also stuck with mate boosted dragons that can't even mate properly!

We did a lot of extensive testing and still couldn't find any potential cause or fix.